Estimating the thermodynamic equilibrium constants of metal oxide particles through a general electrophoresis model.

We propose an efficient and convenient procedure for estimating the thermodynamic equilibrium constants of the surface dissociation/association reactions of metal oxide particles through electrophoresis measurements and a general electrophoresis model, which takes account of essentially all the relevant factors. These constants are usually estimated experimentally through a tedious potentiometric acid-base titration procedure. In addition, since several assumptions need be made in applying this procedure, the results obtained can be unreliable, especially when the difference between the equilibrium constant of the dissociation reaction and that of the association reaction is small. Another merit of the procedure proposed is that the site density of the surface dissociation/associations functional groups need not be known in advance so that it becomes much more convenient and efficient than previous procedures. The applicability of the present procedure is examined by applying it to the cases of SiO and TiO nanoparticles dispersed in an aqueous NaCl solution.